They have basically no food and water, and what water they have isn't clean; they also have no anesthetic or ways to keep wounds clean or disinfected and people are losing limbs everywhere; 300,000 is sadly too easy to believe. If the hostages were starving despite Hamas doing everything in their power to keep them alive, then you know the population is even worse off.
Yeah I posted about this in the news megathread months ago. That's when Ralph Nader started saying this in articles that he wrote, which he mentioned in this interview that you have linked. In that article Nader also argued that both sides want to suppress the true death toll to an extent, Hamas and the resistance so they can justify continued fighting, and Israel so they can keep the genocide going and avoid more scrutiny. Nader also states this in the interview.